In line with the Registry's chief function as an educational resource for experimental and toxicologic pathologists, 66 study sets have been sent to scientists throughout the world seeking consultation for various problems in experimental pathology. Sixty-seven consultations have been held at the Registry. A new study set, Hematopathology of the Mouse, is in completion and will be added to the 16 presently available. Cases for this new set have been obtained from numerous laboratories in addition to about 100 mice which have been necropsied to supply lymphoma tissue examined by immunocytochemistry and molecular analyses. Evaluation of the hematoxylin-eosin stained tissues is being reviewed by an international panel of experts. A program has begun to evaluate archival material in Registry files for suitability for immunocytochemical analysis. Test results of frozen sections are used as positive controls for archival tissue. Antigens tested include oncogene and tumor suppressor gene products. These examinations are in progress to see if immunocytochemistry can be used to develop criteria to help to distinguish benign from malignant cancers in animals, in addition to standard morphologic analysis. A program is also underway to evaluate archival material as a source of DNA and RNA for molecular studies. In order to supply the Registry with material from ongoing research, new cases of experimental cancers for entry into the Registry have been located and are being evaluated. These include: collections of rat and hamster tissue from chemical carcinogenesis experiments, plasmacytomas induced in mice by different agents, and xenografts in nude mice. In addition, materials representing neoplasms in transgenic and knockout mice are being sought to add to the Registry and for a new study set.